Collection<String> c = MinimalCollection.of("a", "a", "a");
    Set<String> set = copyOf(c);
    assertEquals(Collections.singleton("a"), set);
  }

  public void testCopyOf_collection_general() {
    Collection<String> c = MinimalCollection.of("a", "b", "a");
    Set<String> set = copyOf(c);
    assertEquals(2, set.size());
    assertTrue(set.contains("a"));
    assertTrue(set.contains("b"));
  }

            .named("ForwardingList[ArrayList] with standard implementations")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.ALLOWS_NULL_VALUES,
                ListFeature.GENERAL_PURPOSE)
            .createTestSuite());
    suite.addTest(
        ListTestSuiteBuilder.using(
                new TestStringListGenerator() {

                  @Override

            .named("ForwardingSortedMultiset with standard impls")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.KNOWN_ORDER,
                CollectionFeature.GENERAL_PURPOSE,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    return suite;
  }

  @SuppressWarnings({"rawtypes", "unchecked"})
  public void testForwarding() {

              }
            })
        .named("badly colliding HashSet")
        .withFeatures(
            SetFeature.GENERAL_PURPOSE,
            CollectionFeature.ALLOWS_NULL_VALUES,
            CollectionSize.SEVERAL)
        .suppressing(suppressForHashSet())
        .createTestSuite();
  }

  public Test testsForConcurrentSkipListSetNatural() {

        MultisetTestSuiteBuilder.using(enumMultisetGenerator())
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.KNOWN_ORDER,
                CollectionFeature.GENERAL_PURPOSE,
                CollectionFeature.SUPPORTS_ITERATOR_REMOVE,
                CollectionFeature.ALLOWS_NULL_QUERIES,
                MultisetFeature.ENTRIES_ARE_VIEWS)
            .named("EnumMultiset")

  SUPPORTS_REMOVE,
  SUPPORTS_ITERATOR_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,

  /**
   * Features supported by general-purpose collections - everything but {@link #RESTRICTS_ELEMENTS}.
   *
   * @see java.util.Collection the definition of general-purpose collections.
   */
  GENERAL_PURPOSE(SUPPORTS_ADD, SUPPORTS_REMOVE, SUPPORTS_ITERATOR_REMOVE),

  /** Features supported by collections where only removal is allowed. */

 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum SetFeature implements Feature<Set> {
  GENERAL_PURPOSE(CollectionFeature.GENERAL_PURPOSE);

  private final Set<Feature<? super Set>> implied;

  SetFeature(Feature<? super Set>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override

            .withFeatures(
                MapFeature.ALLOWS_NULL_KEYS,
                MapFeature.ALLOWS_NULL_VALUES,
                MapFeature.ALLOWS_ANY_NULL_QUERIES,
                MapFeature.GENERAL_PURPOSE,
                MapFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION,
                CollectionFeature.SUPPORTS_ITERATOR_REMOVE,
                CollectionSize.ANY)
            .createTestSuite());

@GwtCompatible
public enum ListFeature implements Feature<List> {
  SUPPORTS_SET,
  SUPPORTS_ADD_WITH_INDEX(CollectionFeature.SUPPORTS_ADD),
  SUPPORTS_REMOVE_WITH_INDEX(CollectionFeature.SUPPORTS_REMOVE),

  GENERAL_PURPOSE(
      CollectionFeature.GENERAL_PURPOSE,
      SUPPORTS_SET,
      SUPPORTS_ADD_WITH_INDEX,
      SUPPORTS_REMOVE_WITH_INDEX),

  /** Features supported by lists where only removal is allowed. */

 * Implementations of this interface should avoid performing blocking calls or synchronizing on
 * shared resources.
 *
 * @param <K> the most general type of keys this listener can listen for; for example {@code Object}
 *     if any key is acceptable
 * @param <V> the most general type of values this listener can listen for; for example {@code
 *     Object} if any key is acceptable
 * @author Charles Fry
 * @since 10.0
 */